1. Field of the Invention
The present invention relates to a converter having an address translation function and a communication control system in a network system including such a converter.
2. Description of the Related Art
In the past, as a network system for transmitting various types of data, for example, an asynchronous transfer mode (ATM) network, Ethernet® network (hereinafter explained as a “local area network (LAN)” or “wide area LAN”), etc. are known. An ATM network breaks down data into 48-byte cells, adds 5-byte headers to these, and transmits the resultant 53-byte cells. It transmits the data to the opposing side at a high speed in accordance with virtual path identifiers (VPI) and virtual channel identifiers (VCI) at headers of the cells. Further, a LAN adds the source address and destination address to the headers to compose frames for transmission. For example, there are known the 100BASE-FX, 100BASE-T, 1000BASE-LX, 1000BASE-SX, 10GBASE-X, and other specifications of the IEEE802.3 standard.
Further, in a LAN, each terminal is assigned a media access control (MAC) address. This MAC address is used as a destination address when composing and transmitting a frame of data. Further, in a wide area LAN, terminals positioned at geographically separated sites are connected through bridges etc. arranged at those sites and provided with required transmission capabilities. Note that for efficiently forwarding communication data constituted by Internet protocol (IP) packets with nonspecific MAC addresses, one method is to provide an address table in each bridge to provide a function of translating between IP addresses and MAC addresses. When constructing such an address table, as an address resolving means spanning transmission layers, for example, there is known the means of utilizing an address resolution protocol (ARP) to acquire the MAC address of a destination (for example, see Japanese Unexamined Patent Publication (Kokai) No. 2002-319953).
Summarizing the problems to be solved by the invention, the above-mentioned ATM network transmits cells of data in accordance with the VPI/VCIs attached to the headers. It has various advantages, but the cost of maintenance of lines connecting a plurality of ATM exchanges or a plurality of sites is high, so there is the problem of increased costs. As opposed to this, the above-mentioned LAN can maintain multipoint-to-multipoint lines at a relatively low cost and does not include any expensive exchanges, so there is the advantage that the costs can be reduced. Therefore, it has been proposed to form part of each ATM network by a LAN (in particular a wide area LAN) and connect a plurality of such ATM exchanges through the LAN to construct a network system. In this case, means of translating between the VPI/VCIs attached to the headers of the cells in the ATM networks and the MAC addresses attached to the frames in the LAN, that is, address resolving means, become necessary.
Therefore, it may be considered to provide a MAC address management server. However, a MAC address management server would be relatively expensive and would have to be provided for each ATM exchange, so there would be the problem that even use of a LAN would not enable the costs to be sufficiently reduced. Note that for the MAC address translation of a bridge in the prior art, only a means for translating between an IP address and MAC address is shown. An ATM network has not been considered at all.